With the advent of electronic business communication systems, there is now available a business communication system in which only a fixed number of wires need be cabled out to the key telephone set regardless of the number of line pickup keys with which the set is equipped. This reduction in the number of conductors has been made possible by the dedication of certain of the wires in the cable for voice communication and certain others of the wires for only data communications functions such as transmitting lamp or ringer control signals, key button status, and call signalling information. The operated key button identity is transmitted over the data communication conductors and employed by the business communication system central processing unit to control the switching network to connect the voice communication (tip and ring) conductors of the key telephone set with the designated line. The central processor unit provides control signals for the establishment of the requisite network connections and also transmits the needed lamp and ringer control data to the key telephone station sets over the data communication conductors.
Such a system is predicated on the use of electronic key telephone sets, which contain the sophisticated electronic circuitry to communicate with the central processor unit via the data communication conductors. However, many business customers do not require multiple line pickup at every station set in the business communication system. There are numerous instances when certain stations need only a call origination and/or a call reception capability. In these situations, provision of the electronic key telephone sets with sophisticated circuitry and the associated wide range of features is not only undesirable but also uneconomical.
A certain amount of cost savings can be obtained by replacing the electronic key telephone sets with a conventional nonkey telephone station set, which provides only a call origination and a call reception capability. In doing so a problem is presented in that, while the conventional nonkey telephone station set is connectable to the dedicated voice communication conductors, there are no provisions for terminating the electronic business communication system data communication conductors.
One solution to this difficulty is the provision of a special nonkey line circuit in the electronic business communication system in place of the standard line circuit to interface the conventional two wire nonkey telephone station set with the business communication system. Prior art patents such as D. G. Medill, U.S. Pat. No. 3,789,152 issued Jan. 29, 1974 and D. G. Medill, U.S. Pat. No. 3,789,154 issued Jan. 29, 1974 teach such an arrangement. These prior art patents teach restricting the services available to certain stations to only a call origination and a call reception capability by providing these subscribers with conventional nonkey telephone station sets and special nonkey line circuits.
The Medill special nonkey line circuits convert the on-hook/off-hook idle/busy status indications appearing on the two wires of the conventional nonkey telephone station set to the digital bit stream data format required by the electronic business communication system. The special nonkey line circuit also decodes the electronic business communication system control data signals to detect signals indicative of ringing. If a ringing indication is detected, the special nonkey line circuit places a 20 cycle 90 volt ringing signal on the tip and ring conductors of the conventional nonkey tip and ring conductors of the conventional nonkey telephone station set.
Thus, these prior art special nonkey line circuits interface the low voltage digital data bit stream format employed by the electronic business communication system with the high voltage ringing and loop supervision environment of the conventional nonkey telephone station sets. The disadvantage of these prior art inerface arrangements is that each time a nonkey telephone station set is moved to another location, a telephone company craftsperson must replace the standard electronic business communication system line circuit with the special nonkey line circuit to provide an appropriate interface with the electronic business communication system. Thus, some of the cost savings inherent in the use of an inexpensive telephone station set is offset by the necessity of having a craftsperson rearrange line circuits each time a telephone station set is relocated.
An alternative to the use of special line circuits is the provision of an interface circuit in or near each conventional nonkey telephone station set. These modified conventional nonkey telephone station sets would then be connected to the standard electronic business communication line circuit. However, prior art interface circuits are incapable of being located in the conventional nonkey telephone station set due to their complex structure. The complexity of these prior art interface circuits stems from the fact that these interface circuits received and decode the digital data bit streams which comprise the control data transmitted by the business communication system to the interface circuit. In addition, these interface circuits generate and transmit an appropriately responsive digital data bit stream to provide status information to the business communication system. The decoding, interpretation and generation of these digital data bit streams requires complex logic and timing circuitry thus nullifying the economic benefits obtained by using a conventional nonkey telephone station set.
In view of the foregoing, it is an object of this invention to provide circuitry in electronic business communication systems to enable conventional nonkey telephone station sets to be interchanged with electronic key telephone sets without requiring extensive manipulation of circuitry or the continual reprogramming of the electronic business communication system central processing unit.
It is also an object of this invention to enable the interchange of electronic key telephone station sets and conventional nonkey station sets without requiring the intervention of a telephone company craftsperson.
It is a further object of this invention to provide an interface circuit which provides station signalling without resorting to the use of high voltage ringing signals.
It is a further object of this invention to provide an interface circuit locatable in the conventional nonkey telephone station set itself and operable from power supplied over the data communication conductors.
It is a further object of this invention to provide a interface circuit that is of less cost and complexity than prior art circuit arrangements.